Analytical and numerical modelling of pseudo-horizontal jet fires of hydrocarbon gases

Jet fires, turbulent diffusion flames resulting from accidental releases, are associated with a significant hazard due to their intense localised thermal load. The high burning rate, caused by the turbulent mixing of fuel and air, can exert thermal stress on people, equipment and structures. Moreover, it may trigger domino effects, leading to severe escalations from the initial event. Current industrial safety practices address the problem by estimating the peak radiation flux through well-established analytical formulations, followed by existing closed-form semiempirical formulations to calculate the time-to-failure calibrated for specific industrial equipment. However, this approach is not of general applicability, and both designers and surveillance bodies are currently not provided with reliable methodologies to extend the calibrated formulations to general cases, nor with the instruments to perform probabilistic analysis. The methodological approach of this study, inspired and funded by the Italian Civil Protection Department, aims to fill this gap. The thermal load on a generic component exposed to jet fire from light alkanes is evaluated through time histories of radiative flux from flawed long pressurised steel pipelines or pressurised tanks. Systematic comparison with alternative methods is carried out, including both analytical and numerical formulations of the view factor, and computational thermo-fluid-dynamics simulations.